linux-kernel - Re: [PATCH v5 0/3] Add Qualcomm PCIe Endpoint driver support

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Message-ID: <20210712075302.GA8113@workstation>
Date:   Mon, 12 Jul 2021 13:23:02 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        devicetree@...r.kernel.org, PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        hemantk@...eaurora.org,
        Siddartha Mohanadoss <smohanad@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sriharsha Allenki <sallenki@...eaurora.org>,
        skananth@...eaurora.org, vpernami@...eaurora.org,
        Veerabhadrarao Badiganti <vbadigan@...eaurora.org>
Subject: Re: [PATCH v5 0/3] Add Qualcomm PCIe Endpoint driver support

On Thu, Jul 01, 2021 at 09:25:01AM -0600, Rob Herring wrote:
> On Tue, Jun 29, 2021 at 9:47 PM Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> >
> > Hello,
> >
> > This series adds support for Qualcomm PCIe Endpoint controller found
> > in platforms like SDX55. The Endpoint controller is based on the designware
> > core with additional Qualcomm wrappers around the core.
> >
> > The driver is added separately unlike other Designware based drivers that
> > combine RC and EP in a single driver. This is done to avoid complexity and
> > to maintain this driver autonomously.
> >
> > The driver has been validated with an out of tree MHI function driver on
> > SDX55 based Telit FN980 EVB connected to x86 host machine over PCIe.
> >
> > Thanks,
> > Mani
> >
> > Changes in v5:
> >
> > * Removed the DBI register settings that are not needed
> > * Used the standard definitions available in pci_regs.h
> > * Added defines for all the register fields
> > * Removed the left over code from previous iteration
> >
> > Changes in v4:
> >
> > * Removed the active_config settings needed for IPA integration
> > * Switched to writel for couple of relaxed versions that sneaked in
> 
> I thought we resolved this discussion. Use _relaxed variants unless
> you need the stronger ones.
> 

I thought the discussion was resolved in favor of using read/writel. Here
is the last reply from Bjorn:

"I think we came to the conclusion that writel() was better
than incorrect use of writel_relaxed() followed by wmb(). And in this
particular case it's definitely not happening in a hot code path..."

IMO, it is safer to use readl/writel calls than the relaxed variants.
And so far the un-written rule I assumed is, only consider using the
relaxed variants if the code is in hot path (but somehow I used the
relaxed version in v1 :P )

Thanks,
Mani

> Rob
> 
> >
> > Changes in v3:
> >
> > * Lot of minor cleanups to the driver patch based on review from Bjorn and Stan.
> > * Noticeable changes are:
> >   - Got rid of _relaxed calls and used readl/writel
> >   - Got rid of separate TCSR memory region and used syscon for getting the
> >     register offsets for Perst registers
> >   - Changed the wake gpio handling logic
> >   - Added remove() callback and removed "suppress_bind_attrs"
> >   - stop_link() callback now just disables PERST IRQ
> > * Added MMIO region and doorbell interrupt to the binding
> > * Added logic to write MMIO physicall address to MHI base address as it is
> >   for the function driver to work
> >
> > Changes in v2:
> >
> > * Addressed the comments from Rob on bindings patch
> > * Modified the driver as per binding change
> > * Fixed the warnings reported by Kbuild bot
> > * Removed the PERST# "enable_irq" call from probe()
> >
> > Manivannan Sadhasivam (3):
> >   dt-bindings: pci: Add devicetree binding for Qualcomm PCIe EP
> >     controller
> >   PCI: dwc: Add Qualcomm PCIe Endpoint controller driver
> >   MAINTAINERS: Add entry for Qualcomm PCIe Endpoint driver and binding
> >
> >  .../devicetree/bindings/pci/qcom,pcie-ep.yaml | 160 ++++
> >  MAINTAINERS                                   |  10 +-
> >  drivers/pci/controller/dwc/Kconfig            |  10 +
> >  drivers/pci/controller/dwc/Makefile           |   1 +
> >  drivers/pci/controller/dwc/pcie-qcom-ep.c     | 742 ++++++++++++++++++
> >  5 files changed, 922 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/devicetree/bindings/pci/qcom,pcie-ep.yaml
> >  create mode 100644 drivers/pci/controller/dwc/pcie-qcom-ep.c
> >
> > --
> > 2.25.1
> >